Re-planning in Gamma Knife radiotherapy Centre

Gamma knife, stereotaktička radioneurokirurška metoda, se razvija godinama kako bi omogućila liječenje intrakranijalnih lezija bez klasičnog otvaranja lubanje kirurškim putem. Razvoj Elektinog Icon uređaja s integriranim „cone-beam“ CT uređajem pruža nove mogućnosti. „Cone-beam“ CT se smatra najtočnijim modalitetom za definiciju stereotaktičkog prostora. Iako je primarno namijenjen za definiciju stereotaktičkog prostora kod pacijenata kojima se za fiksaciju koristi termoplastična maska, CBCT se može primjeniti i za korekciju položaja tumora kada se koristi Leksellov stereotaktički okvir. Cilj: Cilj rada je prikazati učestalost replaniranja tumora u svakodnevnom radu, istražiti u kojim slučajevima su terapijski planovi bili replanirani, u kakvom je to odnosu s veličinom i/ili položajem tumora u prostoru i objasniti kliničku važnost adekvatnih protokola planiranja i korištenja “cone beam” CT-a. Metode: Pri izradi ovog rada, korišteni su dozimetrijski podatci uzeti iz Gamma Plana programa za planiranje, retrospektivno, nakon izvršenog postupka na pacijentima. Analizirani su podatci 50 pacijenata s dijagnozom solitarne metastaze mozga i 50 pacijenata s dijagnozom vestibularnog švanoma. Ulazni podatci poput pokrivenosti, anatomskog pomaka, volumena i histologije tumora su korelirani s učestalosti replaniranja, a statistička značajnost je dobivena pomoću t-testa. Rezultati: Analiza podaka je pokazala da vjerojatnost replaniranja ovisi veličini tumora. Vjerojatnost replaniranja je veća za manje tumore te je razlika statistički značajna (P=0,009; CI=95). Osim toga, analiza je pokazala da vjerojatnost replaniranja ne ovisi o udaljenosti tumora od centra stereotaktičkog prostora (P=0,865; CI=95) i da vjerojatnost replaniranja ne ovisi o histologiji tumora (P=0,6; CI=95). Od 100 pacijenata, ukupno je replanirano 26 % planova, od toga 28 % planova za metastazu i 24 % planova za vestibularni švanom. Zaključak: Korekcija položaja i replaniranje korištenjem “cone-beam” CT-a u procesu rada u stereotaktičkoj radiokirurgiji, se pokazalo kao dobra metoda koja omogućava pravilnu isporuku doze na tumor te na taj način poboljšava kvalitetu liječenja.Gamma knife, stereotactic radiosurgery method, has evolved over the years to allow non-open surgical treatment of intracranial pathologies. New Elekta Icon Gamma Knife model comes with integrated cone-beam CT. Cone-beam CT is considered the most accurate modality for coordinate definition of stereotactic space. Primary purpose of CBCT is definition of stereotactic space for frameless treatment where thermoplastic mask is used to immobilize patient’s head. Besides that, it is very usefull for tumor position correction when Leksell stereotactic frame is used. Purpose: The aim of this paper is to show the frequency of re-planning in daily work, to invesrtigate in which cases the treatment plans were re-planned, what is relation between coverage decrease and volume or between tumor location in stereotactic space and what is clinical importance of re-planning. Methods: In preparing this paper, dosimetric data taken from the Gamma Plan planning program were used retrospectively, after the procedure was performed on patients. Data for 50 patients diagnosed with solitary brain metastasis and for 50 patients diagnosed with vestibular schwannoma were analyzed. Input data such as coverage, anatomical displacement, volume, and tumor histology were correlated with re-planning frequency, and statistical significance was obtained using a t-test. Results: Data analysis showed that the chance of re-planning depends on the size of the tumor. The chance of re-planning is higher for smaller tumors and the difference is statistically significant (P = 0.009; CI = 95). In addition, the analysis showed that the chance of re-planning did not depend on the distance of the tumor from the center of the stereotactic space (P = 0.865; CI = 95) and that the chance of re-planning did not depend on tumor histology (P = 0.6; CI = 95). Out of 100 patients, a total of 26% of the plans werere-planned, of which 28% were plans for metastasis and 24% were plans for vestibular schwannoma. Conclusion: Position correction and re-planning using cone-beam CT, in the process of work in stereotactic radiosurgery, has proven to be a good method that allows proper delivery of the dose to the tumor and thus improves the quality of treatment